1. Field of the Invention
The present invention relates generally to communications systems and more specifically to a method and system for transmission and reception of asynchronously (statically) multiplexed signals onto a common transmission medium. The present invention is particularly useful for asynchronously multiplexing data units of different format such as ATM cells and frames (i.e., layer-2 frames) in which IP (Internet Protocol) packets are encapsulated.
2. Description of the Related Art
Demand for high speed communication systems is increasing to meet multimedia communications services (audio, video and the Internet). Physical interfaces for implementing high speed communications have been deployed to provide a wide range of different services corresponding to networks of different architecture. For multimedia communications, ATM (asynchronous transfer mode) cells are the most promising data format for transporting user traffic as a multimedia platform. In addition, high-speed transport interfaces are increasingly used for interfacing high-capacity routers. However, there is an increasing amount of processing burden on the transport interfaces for assembling data traffic into ATM cells and disassembling ATM cells to original format. The transport interfaces thus represent a bottleneck for high speed transmission. One solution to this problem is the use of point-to-point protocol (PPP) frames in the transport interface. However, a need will arise to multiplex PPP frames with ATM cells over a transmission system such as SONET (synchronous optical network. Because of their difference in data format, PPP frames and ATM cells must be segmented into bytes and alternately multiplexed onto synchronized time slots. However, it is impossible to control the allocated bandwidths according to traffic needs. Alternatively, WDM (wavelength division multiplexing) technique may be used to carry PPP frames and ATM cells on different wavelengths to be multiplexed onto a common optical link. However, efficient resource utilization cannot be achieved because of the inability to control the allocated bandwidth according to varying traffic. In addition, the use of two wavelengths represents a waste of one wavelength which could be otherwise used for other high speed traffic.
In addition, a need may exist for asynchronously multiplexing data units of same format but different lengths.